Electron beam projector provided with a linear thermionic emitting cathode for electron beam heating

ABSTRACT

An electron beam gun comprises a beam waveguide and an accelerating anode fixed thereto. The accelerating anode is connected with the aid of high-voltage insulators and through a cathode plate to a cathode assembly. The cathode assembly comprises a linear hot cathode fixed with the aid of two cathode carriers and a focussing electrode which is coaxially arranged with respect to the linear hot cathode and encompasses it with the aid of a two-sided surface. The beam waveguide is separated from the accelerating anode with the aid of rack panels which rigidly fix the accelerating anode to the beam waveguide in such a way that a space is formed therebetween. In order to hermetically separate cathode and anode parts of the projector, the accelerating anode is provided with a plate rigidly connected thereto.

FIELD OF THE INVENTION

The invention pertains to apparatuses of electron beam technology, ormore specifically to electron guns for electron beam heating, meltingand evaporation of materials in vacuum or reactive gas atmosphere.

PRIOR ART

Electron guns with a linear hot cathode of 100–150 kW power have smalldimensions, are convenient in operation and are widely used inproduction electron beam units for various applications and described inarticle by B. A. Movchan, V. A. Timashov. “Plane Beam Electron Guns forMelting and Evaporation of Materials”, in the book “Refining Remelting”,K., Naukova Dumka, 1975, pp. 131–139; in the book by G. B. Stroganov, V.M. Chepkin, V. S. Terentjeva “High-temperature Resistant Coatings forGas Turbines”, M., “Navigator-extra” Publ. House, 2000.

Production electron beam units are widely used for producing variouscoatings and materials both in vacuum environment and in reactive gasenvironment.

Known are electron guns with a linear hot cathode, developed by E.O.Paton Electric Welding Institute of the NAS of Ukraine (U.S. Pat. No.3,814,829, 1974, IPC N05b 7/00; USSR Auth. Cert. #686158, 1979, IPC B 05B 7/00, H01J 3706; U.S. Pat. No. 4,105,890, 1978, IPC B23K 9/00; Patentof Ukraine #21440A, 1997, IPC H01J 29/46, 29/48). They are capable ofdeflecting the beam by 25–45 degr., being located at a considerabledistance from materials being heated and in separate gun chambers, whichhave individual pumping down means. This enables their successfulapplication in production electron beam units, both for working in avacuum environment and in a reactive gas environment.

The main problem in the majority of known guns with a linear hot cathodeis a short duration of continuous gun operation without hot cathodereplacement in the reactive gas environment, insufficient stability ofthe specified parameters of the electron beam on the surface ofmaterials being heated during long-term operation of the gun.

A short duration of continuous operation of the gun with a linear hotcathode in the reactive gas environment is due to intensive ionbombardment of the linear hot cathode, resulting from ionisation of thegas flow, which is the most pronounced in operation at a high pressureof reactive gases.

Ion bombardment leads to local overheating, sputtering of the linear hotcathode surface, which results in its service life becoming muchshorter.

Designs of axial guns, which allow solving the problems of extending thecathode service life, are known and described in the book by Z. Shiller,W. Geising, Z. Paptser, “Electron Beam Technology”, transl. From German,M, “Energia”, 1980. For guns with a linear hot cathode this problem isstill unsolved.

Insufficient stability of the specified parameters of the electron beamon the surface of materials, which are heated, is due to unstableposition of the linear hot cathode relative to the focusing electrode,because of heating of fixture parts and tension of linear hot cathode.

Change of the linear hot cathode position relative to focusing electrodeleads to a change in the convergence of the electron beam, which resultsin a change of specific power of the beam in the focal spot.

Such changes in the gun operation impair the stability and thereproducibility of the processes of heating, melting and evaporation ofmaterials.

In the known most perfect designs of electron guns with a linear hotcathode, developed by E.O. Paton Electric Welding Institute (U.S. Pat.No. 3,814,829, 1974; USSR Auth. Cert. #686158, 1979; U.S. Pat. No.4,105,890, 1978, Ukrainian Patent #21440A, 1997), an accelerating anodeis used, which is fastened directly on the beam guide and cathode unit,which contains one linear hot cathode, heated by electric currentflowing through it, and special fastening and tension devices providecurrent supply and tension of the linear hot cathode during the gunoperation.

Known is the electron gun with a linear hot cathode, described in U.S.Pat. No. 4,126,811, 1978, IPC H01J 29/46, H01J 29/48. Electron guncontains an accelerating anode, connected to cathode assembly byhigh-voltage insulators. Cathode assembly includes a linear hot cathode,fastened in cathode-holders on the case and positioned co-axially withthe focusing electrode. One face side of the hot cathode is turnedtowards the accelerating anode, the other is positioned with a gaprelative to the focusing electrode, which encloses the hot cathode by atwo-face surface. Focusing electrode is made in the form of two parts,mounted with a gap. The ends of two flat springs are fastened to theopposite end faces of these parts; other ends of the springs areconnected to a terminal current supply for feeding the filament current.The ends of two more flat springs are fastened in cathode holders to theother ends faces of the parts, these ends being electrically coupled tocurrent supplies and fastened on the insulator of the cathode assemblycasing. Such design of the gun does not provide a high reproducibilityor stability of the position of the linear hot cathode relative to thefocusing electrode, because of the difficulties of precise fixing withscrew joints the relative position of the two parts of the focusingelectrode and linear hot cathode, and in heating of the gun parts duringlong-term operation. It does not solve the problem of extending theservice life of the linear hot cathode.

Known is an electron beam gun described in U.S. Pat. No. 4,105,890,1978, IPC B23C 9/00, which allows deflecting the electron beam by an upto 45 degr. angle, by using additional focusing coils in the gun beamguide part. This improves the protection of the linear hot cathode andthe focusing electrode from penetration of direct vapour flows ofmaterials, which evaporate, but does not solve the problem of stabilityof the linear hot cathode position relative to the focusing electrode orreducing ion bombardment of the linear hot cathode.

Known is an electron gun with a linear hot cathode, described in theUkrainian application for invention #97074063, IPC H0J 29/46, 29/48,37/04 (“Promyslova Vlastnist” Bulletin #8(1), 1999). Electron guncontains the anode and cathode assemblies, connected by a high-voltageinsulator. Anode assembly contains the anode, fastened directly on thebeam guide, which is made in the form of a cylinder of a non-magneticmaterial, and a deflecting system of a circular magnetic core. Cathodeassembly contains: case; flat insulator built into the case; linear hotcathode, which is fastened on the case, using two cathode-holders, oneof which is hinged to the case via a flat insulator; focusing electrodewith a terminal current supply for feeding a regulated potentialnegative relative to the coaxially-mounted linear hot cathode. Springs,which provide the tension of the linear hot cathode, are located at adistance from the hot cathode radiation surface and are notcurrent-coonducting. In the claimed design of the gun the position oflinear hot cathode relative to the focusing electrode is determined bythe accuracy of making the parts, which may be insufficient in view ofthe hinged nature of fastening and long arm to the point of cathodelocation. In addition, in service, as well as a result of the partheating during long-term continuous operation of the gun, the hingefastening of the cathode will become weaker and the stability ofposition of the linear hot cathode, mounted on the long arm relative tothe focusing electrode, will be even lower. Such a design of the gundoes not solve the problem of reducing the intensity of ion bombardmentin operation with reactive gas bleeding.

The closest one in engineering terms to the claimed invention is theelectron beam gun with a linear hot cathode, described in the Ukrainianpatent for invention #21440A, 1997, IPC H01J 29/46, 29/48, by B. A.Movchan, V. A. Timashov, E. L. Piyuk, taken as the closest prior art.Electron beam gun incorporates: beam guide, accelerating anode,connected by high-voltage insulators to the cathode assembly. The anodeis fixed directly on the beam guide. Cathode assembly incorporates theframe, flat insulator, two cathode-holders and focusing electrode. Onecathode-holder is rigidly fixed to the frame by a current-conductingplate. The second cathode-holder via a pair of current-conductingsprings, and the focusing electrode by a hard post, are fastened to theflat insulator, which is built into the frame. Focusing electrode,installed co-axially with the linear hot cathode, enclosing it by atwo-face surface, is connected to the terminal for feeding the focusingvoltage. Pairs of flat current-conducting springs for fastening onecathode-holder and a plate for fastening the second cathode holder, haveelongated holes for the hot cathode adjustment relative to the focusingelectrode. This design of the electron beam gun is characterised by anunstable position of the linear hot cathode relative to the focusingelectrode, which is due to different conditions of fastening of itsends. Current-conducting strings and post, by which the linear hotcathode is fastened, have different weight, are made of differentmaterials and during heating expand to different lengths. Adjustment ofthe position of the linear hot cathode relative to the focusingelectrode before the start of the gun operation, does not provide itsstable position during long-term operation of the gun at differentpowers of the electron beam. In addition, non-uniform heating ofdifferent sides of the long, located close to the edge of the focusingelectrode fastening post occurs during long-term operation of the gun.This leads to its bending out and angular shifting of the focusingelectrode relative to the linear hot cathode. Applying a potential,negative relative to the linear hot cathode, to the focusing electrode,improves the focusing of the electron spot to a smaller degree, thandeterioration of focusing, caused by unstable position of the linear hotcathode relative to the focusing electrode. In addition, when apotential, negative relative to the linear hot cathode, is applied tothe focusing electrode, the electron beam current decreases. Itsrestoration requires increasing the temperature of heating of the linearhot cathode, which leads to shortening of its life. This design of thegun also does not solve the problem of reducing the ion bombardment ofthe hot cathode in operation with reactive gas bleeding.

THE INVENTION ESSENCE

This invention is aimed at solving the problem of creating such a designof the electron gun with the linear hot cathode, which wouldallow:—avoiding the unstable position of the linear hot cathode relativeto the focusing electrode, caused by heating of gun parts duringlong-term operation, by symmetrical arrangement and making of the partsfor fastening, current supply and tension of the linear hot cathode tobe the same from both ends of the linear hot cathode; —reducing ionbombardment of the linear hot cathode by removing the accelerating anodefrom the beam guide and introducing additional high-vacuum pumping downof the anode-beam guide gap.

This aim is achieved by proposing an electron gun with a linear hotcathode for electron beam heating, which incorporates a beam guide withan accelerating anode, fastened to it, which is connected byhigh-voltage insulators via a cathodic plate to the cathode assembly,which incorporates linear hot cathode, fastened in two cathode holders,and focusing electrode, co-axially positioned and enclosing the linearhot cathode by a two-face surface, in which, according to the invention,the beam guide is separated from the accelerating anode, using posts,providing a rigid fixing of the accelerating anode to the beam guide andcreation of a space between them, the accelerating anode incorporating arigidly fastened to it plate for vacuum-tight separation of the cathodeand beam-guide parts of the gun, and the cathode assembly incorporatingtwo similar current supplies, fastened via ring insulators on thefocusing electrode and connected by flat springs and parallel to themcopper current-conducting plates with cathode holders, the cathodeassembly being made and fastened on the cathodic plate, symmetricalrelative to the vertical axis of the focusing electrode.

It is rational to mount under the ring insulators, by which the currentsupplies are fastened to the focusing electrode, the calibrated gaskets,which will allow regulation of the height of the linear hot cathodemounting relative to the focusing electrode.

It is rational to make the holes in the current supplies for mountingthe ring insulators with tolerance, which enables adjustment of theposition of the linear hot cathode relative to the focusing electrode inthe horizontal plane.

In electron guns with a linear hot cathode, the plane-parallel electronbeam, formed by the electric field in the cathode-anode space, divergesafter passing through the anode slot. Therefore, anode removal from thebeam guide leads to increase of the dimensions of electron beam, whichenters the beam guide and deterioration of the electron-opticalparameters of the gun. However, when working with deflection of electronbeam, normally used in electron beam units, the scattered magnetic fieldof the deflection system of the beam guide penetrates beyond its caseand has a focusing impact on the electron beam in the direction of theanode. The diverging? electron beam reduces the angle of divergence,which allows removing the anode from the beam guide to a distance of70–80 mm without any noticeable deterioration of electron-opticalparameters of the gun. This distance is sufficient to implementadditional high-vacuum pumping down of the space between the anode andbeam guide.

The claimed design allows improvement of the stability ofelectron-optical parameters during long-term operation of the gun, andextension of the duration of continuous operation of the gun, both invacuum environment and in the reactive gas atmosphere.

BRIEF DESCRIPTION OF DRAWINGS

The invention is explained in a detailed description with reference tothe appended drawings:

FIG. 1—General view of the electron gun with a linear hot cathode forelectron beam heating, according to the invention, cut-away drawing.

FIG. 2—Cathode assembly of electron gun with the linear hot cathode forelectron beam heating, according to the invention, cut-away drawing.

DETAIL DESCRIPTION OF THE INVENTION

The claimed electron gun with a linear hot cathode for electron beamheating consists of beam guide 1, which incorporates deflection system16, and to the case of which accelerating anode 2 is fastened by posts13, which incorporates plate 14, which separates the cathode and beamparts of the electron gun, and which is connected by high-voltageinsulators 3 through cathodic plate 4 to cathode assembly 5 (FIG. 1).

Cathode assembly (FIG. 2) consists of focusing electrode 12, to whichtwo current supplies 10 are fastened by retainer screws 17 through ringinsulators 11, with terminals 18 for applying filament voltage to linearhot cathode. Linear hot cathode 6 is fastened in cathode-holders 7,connected to current supplies 10 by screw joints 19 through a system oftension and current supply, which consists of copper plates 9 and flatsprings 8. Linear hot cathode 6 is fixed in cathode-holders 7 by insert20, using screws 21. Limiting posts 22 are mounted to prevent possibleshort-circuiting of filament voltage of linear hot cathode. Holes incurrent supplies 10 to accommodate ring insulators 11 are made with anallowance for horizontal adjustment of the position of cathode holders 7with linear hot cathode 6 fastened in them relative to focusingelectrode 12. The height of the linear hot cathode positioning relativeto the focusing electrode may be adjusted by the number of calibratedgaskets 15 under ring insulators 11.

As it is seen from appended drawings and the above description, in theclaimed design of electron gun with a linear hot cathode, unlike theactual prototype design, the assemblies for fastening both the ends ofthe linear hot cathode and applying filament voltage to them are made tobe the same and symmetrically located relative to the focusingelectrode, the anode is removed from the beam guide system to thedistance, which is determined by the height of the fastening posts, andthe separating plate allows vacuum-tight separation of the gun cathodepart from its beam guide part.

The above device operates as follows.

When the gun of the claimed design is mounted in the electron beam unit,it is necessary to separate by a shield, which is fastened on separatingplate 14, the cathode part of the chamber, accommodating the gun, fromthe beam guide part and set up separate high-vacuum pumping of bothparts of the chamber. Total cross-section of open holes between the mainchamber and the beam guide part of the gun chamber is larger, than thatbetween the two parts of the gun chamber, so that the capacity of themeans of high-vacuum pumping of the beam guide part of the chambershould be higher than of those for the cathode part.

When voltage from the filament source is applied to terminals 18 ofcurrent supplies 10 (FIG. 2), filament current, passing throughcurrent-carrying copper plates 9, cathode-holders 7 and linear hotcathode 6, heats it to the temperature, at which electron emission isobserved. The linear cathode becomes longer. Flat molybdenum springs 8apply a longitudinal tensile force to linear hot cathode and at itselongation allow maintaining the hot cathode linearity and its positionrelative to focusing electrode 12. Change of the dimensions of currentsupplies, flat springs, cathode holders, resulting from gun heatingduring long-term operation, is the same at both ends of linear hotcathode, so that the position of linear hot cathode relative to thefocusing electrode is more stable in the claimed gun than in the closestprior art design.

Specified position of linear hot cathode 6 relative to focusingelectrode 12, required for optimal mode of gun operation, is provided atthe assembly stage by adjustment of the position of current supplies 10and by their fastening with screws 17, as well as by selection of thenumber of calibrated gaskets 15 under ring insulators 11. If required, apotential negative relative to the potential of linear hot cathode isapplied to focusing electrode 12 for final focusing of the focal spot.

On the whole, the claimed electron beam gun provides a longer continuousoperation, higher stability of electron-optical parameters, whichessentially improves the stability and reproducibility of thetechnological processes of melting and evaporation of various materials.The greatest effect from application of the claimed electron gun ismanifested in the cases, requiring long continuous operation of the gunand high stability of its electron-optical parameters. Application ofthe claimed gun is particularly important, when conducting the processesof melting and evaporation in the reactive and inert gas atmosphere.

1. Electron gum with a linear hot cathode for electron beam heating, which comprises a beam guide (1) with an accelerating anode (2) fastened on it, wherein the anode is connected to high-voltage insulators (3) through a cathodic plate (4) with a cathode assembly (5), wherein the cathode assembly comprises a linear hot cathode (6), fastened in two cathode-holders (7), and a focusing electrode (12), mounted co-axially and enclosing said linear hot cathode (6) by a two-face surface, characterized in that said beam guide (1) is separated from said accelerating anode (2) by posts (13), providing a rigid fastening of the accelerating anode on the beam guide and creation of a space between them, said accelerating anode incorporating a plate (14) rigidly connected to it for a vacuum-tight separation of the cathode and the beam guide part of the gun, and the cathode assembly (5) incorporating two similar current supplies (10) fixed to said focusing electrode (12) through ring insulators (11) and connected to the cathode-holders (7) by means of four flat springs (8) and copper current-conducting plates (9) that are located parallel to the flat springs (8), the cathode assembly (5) being made and fastened on the cathode plate 4 symmetrically relative to a vertical axis of focusing electrode (12).
 2. Electron gun according to claim 1, characterized in that it further comprises calibrated gaskets (15) located under the ring insulators (11) of the current supplies (10) mounted on the focusing electrode (12) to enable adjustment of the height of the linear hot cathode (6) relative to the focusing electrode (12).
 3. Electron gun according to claim 1, characterized in that the current supplies (10) contain holes (23), made with tolerance with respect to the ring insulators to enable adjustment of the position of the linear hot cathode (6) relative to the focusing electrode (12) in the horizontal plane. 